ATMOSPHERIC PHENOMENA. 207 
ealms, and furious currents of the atmosphere from 
the south-east and south-west, accompanied with a 
cloudy sky. While the breeze from the north-east 
blows, it prevents the atmosphere from being satu- 
rated with moisture. The hot and loaded air of the 
torrid zone rises and flows off again towards the 
poles, while inferior currents from these last, bring- 
ing drier and colder strata, take the place of the 
ascending columns. In this manner the humidity, 
being prevented from accumulating, passes off to- 
wards the temperate and colder regions, so that the 
sky is always clear. When the sun, entering the 
northern signs, rises towards the zenith, the breeze 
from the north-east softens, and at length ceases; 
this being the season at which the difference of 
temperature between the tropics and the contigu- 
ous zone is least. The column of air resting on 
the equinoctial zone becomes replete with vapours, 
because it is no longer renewed by the current 
from the pole; clouds form in this atmosphere, sa- 
turated and cooled by the effects of radiation and 
the dilatation of the ascending air, which increases 
its capacity for heat in proportion as it is rarefied. 
Electricity accumulates in the higher regions in con- 
sequence of the formation of the vesicular vapours, 
the precipitation of which is constant during the 
day, but generally ceases at night. The showers 
are more violent, and accompanied with electrical 
explosions, shortly after the maximum of the diur- 
nal heat. These phenomena continue until the sun 
enters the southern signs, when the polar current is 
re-established, because the difference between the 
heat of the equinoctial and temperate regions is daily 
increasing. The air of the tropics being thus re- 
